Gas delivery systems typically include a source of gas, such as oxygen, a regulator for reducing the source pressure of the oxygen to a pressure more suitable for use within the delivery system, and a gas line, typically a cannula, for delivering oxygen from the delivery system to the person. Oxygen delivery systems are used not only in hospitals and health care institutions, but also in home-health care and by ambulatory persons requiring oxygen for any number of reasons. Wherever such oxygen delivery systems are used, it is frequently desirable to increase the life of the oxygen supply. This is especially the case in home-based or ambulatory settings where the supply of oxygen is often an oxygen bottle or other relatively finite oxygen source.
To increase the life of the oxygen supply, oxygen conserving devices, also known as oxygen conservers, are frequently used. These conserving devices generally interrupt the flow of oxygen delivered to the person at regular intervals, thereby reducing the rate of oxygen consumption.
Conservers are generally of two types, those which operate electronically, and those which operate pneumatically. Each of these types suffers from various drawbacks and disadvantages. For example, electronic conservers require a power source, generally a battery, in order to operate, thus necessitating periodic replacement or recharging of the power source.
Electronic oxygen conservers sometimes have further disadvantages related to durability and cost.
Pneumatic oxygen conservers are those which make use of the pressurized gas and its flow within the conserver to intermittently block the delivery of gas to the person. Although such pneumatic conservers generally dispense with the need for power sources and complex electronics, they are oftentimes bulkier.
A further disadvantage of pneumatic systems is that they generally require more complex gas lines or cannulas in order to operate. Examples of such pneumatic conservers and their associated dual-lumen cannulas are disclosed in Myers U.S. Pat. No. 4,044,133 and Carter U.S. Pat. No. 5,360,000. One lumen of the cannula is for supplying oxygen to the person wearing the cannula, whereas the other lumen generally connects to a sensing port on the conserver. The pneumatic conserver generally responds to changes in the pressure in the sensing lumen to provide oxygen to the person during inhalation and to interrupt the flow of oxygen to the person in response to exhalation (when oxygen is typically not needed). Unfortunately, dual lumen cannulas are more difficult to obtain, more expensive, bulkier, and generally heavier than the standard, single lumen cannulas used in electronic conservers and many other medical devices.
As a result of these and other drawbacks, pneumatic oxygen conserving devices have not enjoyed widespread use despite certain advantages of such pneumatic conservers over electronic ones.
The various attempts to overcome the drawbacks of pneumatic conservers have had mixed results and have generated their own drawbacks and disadvantages. For example, although the pneumatic oxygen conserver disclosed in Hoffman U.S. Pat. No. 2,881,725, makes use of a single-lumen cannula, the device disclosed therein does not generally deliver oxygen in a manner consistent with the oxygen consumption profiles of a person breathing through a cannula. In other words, it is desirable for oxygen delivery from a conserving device to match a person's needs for oxygen as closely as possible.
There is a need, therefore, for a pneumatic oxygen conserving device which can be used as part of an oxygen delivery system, and which overcomes the disadvantages of current oxygen delivery systems.